A resist composition for electron beam has been heretofore widely studied on its application to the formation of a semiconductor fine pattern or the formation of a mask pattern for fine pattern projection, and recently, its application to a mold (sometimes referred to as a “stamper” or the like; hereinafter, in the context of the present invention, unless otherwise indicated, the “mold” and the “stamper” have the same meaning) used in an imprint process is also being studied.
As one application, for example, in JP-A-2004-158287 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and JP-A-2008-162101 where a mold structural body or stamper carrier having a concave-convex structure is used in the process of preparing an information recording medium, use of a resist composition in preparing the mold structural body or stamper itself is described. The information recording medium as used herein is a concept including a magnetic recording medium (e.g., hard disk), an optical disk, a magento-optical disk and the like.
Furthermore, a so-called nanoimprint technique is positioned as one of candidate techniques for the formation of a semiconductor microcircuit, particularly an ultrafine semiconductor circuit pattern in the line width generation of 22 nm or less, and also in this technique, studies are being made on the application of an electron beam resist to the preparation of a mold.
For example, in performing reactive ion etching on a substrate, a pattern formed of a resist composition is used as a mask, and the substrate surface is thereby selectively etched to prepare a mold having a concave-convex pattern.
Also, in preparing a mold by a procedure of (1) forming a concave-convex pattern on a substrate such as silicon (Si) substrate, which is disadvantageous in view of strength and life but is excellent in terms of processability such as reaction ion etching (RIE), to prepare a mold (sometimes referred to as a “master mold”), and (2) then transferring the pattern of the master mold to a substrate having higher durability, thereby preparing a plurality of practically endurable molds (sometimes referred to as a “replica mold”), a pattern formed of a resist composition for electron beam is utilized as the mask for RIE in (1).
As one example of this method, a method of preparing an Ni mold (replica mold) by electroformation using an Si mold as the master mold is disclosed in Science and New Technology in Nanoimprint, edited by Yoshihiko Hirai, Frontier Publishing, page 30 or 60.
Here, in the pattern formation by electron beam irradiation, correction of a so-called “proximity effect” is important. The proximity effect is a problem that electrons collided against a carrier are scattered in the proximity to cause formation of a latent image even in an unirradiated portion and a desired pattern cannot be obtained. In the application to the conventional formation of a semiconductor fine pattern, this effect at the pattern drawing by scanning in the x-y direction can be reduced to a certain extent by virtue of development of devices.
On the other hand, in the preparation of, for example, the above-described mold structural body or stamper carrier having a concave-convex structure, which is used in the preparation of an information recording medium, it is proposed in the documents above to perform the exposure by scanning an electron beam in the r-O direction on a discotic substrate. Scanning in the r-θ direction also requires to solve the problem of proximity effect not only from the device side but also from the resist material side.
Furthermore, also in the pattern drawing by scanning in, the x-y direction, the electron beam resist is required to be more enhanced in its performance so as to form an ultrafine pattern for nanoimprint. Because, in the application to the formation of a mask pattern for lithography, which is the main application of the conventional resist composition for electron beam, the formation of a final semiconductor circuit is performed by so-called reduction exposure and therefore, a mask pattern having an approximately double size compared with the pattern size, if it could be prepared, can be used in practice, whereas the nanoimprint process allows in principle only for pattern transfer at the same magnification and a pattern having a line width in the 20 nm order must be satisfactorily formed at the stamper preparation stage.